To increase data storage and retrieval performance, many digital linear magnetic tape recording systems utilize multi-head, multi-channel fixed head structures with narrowed recording gaps and track widths so that many linear data tracks may be achieved on a tape medium of predetermined width. Tape substrates are also being made thinner with increased tape lengths in small diameter packages.
Head positioning servo systems are employed in many contexts requiring accurate positioning of a read and/or write head in a magnetic tape system over a selected data track. Misalignment between the head and the data track may cause data errors during read back and data loss on adjacent tracks during writing.
In multi-track magnetic tape storage systems, random lateral tape motion (“LTM”) is a limiting factor in achieving higher densities and thus higher user data capacity per tape. LTM is an undesirable motion of the tape in a lateral direction that is transverse to the tape direction. LTM may be caused by many factors including tape slitting variations, tension variations, imperfections in the guiding mechanism, friction variations in the recording head, and environmental factors such as heat and humidity. These factors affect LTM in various ways. Some cause abrupt momentary jumps of the tape in a directed lateral to its travel, while others may cause small shift in a lateral direction during tape travel. Generally, LTM is unpredictable and unrepeatable and must be compensated for.